This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-371360 filed on Dec. 6, 2000 and Japanese Patent Application No. 2001-308502 filed on Oct. 4, 2001.
1. Field of the Invention
The present invention relates to a dynamo-electric machine, specifically a dynamo-electric machine having brushes for supplying electric power to a commutator and also to a method for manufacturing the same.
2. Description of Related Art
In a dynamo-electric machine (e.g., direct current motor), electric power is supplied to an armature (windings of a core) through brushes that are in sliding contact with an outer peripheral surface (sliding contact surface) of a commutator. Each brush is received in a corresponding brush case integrally formed in a brush holder.
In such a dynamo-electric machine, a roundness of the outer peripheral surface of the commutator, a size of each step formed between corresponding adjacent commutator segments, a deviation between a position of each brush and a corresponding rotational position of the armature (commutator) or the like are the factors that need to be considered to achieve appropriate commutation (restraining the disturbance of the commutation) of the dynamo-electric machine (commutator and brushes) and to restrain deterioration of motor efficiency, generation of vibrations and vibrational noise and/or the like. Thus, in order to restrain the disturbance of the commutation and to restrain the generation of the vibrations and vibrational noise, the roundness of the commutator has been improved by improving processing precision of the commutator to provide an ideal sliding contact surface (uniform sliding contact surface) of the commutator, which is in sliding contact with sliding contact surfaces of the brushes.
By improving the processing precision of the commutator and thereby improving the roundness of the sliding contact surface of the commutator, the vibrations and vibrational noises generated between the commutator and the brushes can be reduced. However, the improvement in the roundness of the sliding contact surface of the commutator pauses another disadvantage. That is, as a result of the improvement in the roundness of the sliding contact surface of the commutator, the sliding contact surface of the commutator closely and tightly fits or sticks with the opposing sliding surface of each brush. This generally causes a phenomenon known as xe2x80x9cstick-slipxe2x80x9d occuring between the commutator and the brushes, and hence rotation of the commutator results in squealing noise generated between the commutator and the brushes and/or abnormal wearing of the brushes.
The present invention addresses the above disadvantages. Thus, it is an objective of the present invention to provide a dynamo-electric machine capable of restraining disturbance of commutation, reduction of motor efficiency, generation of vibrations and vibrational noise in an armature as well as generation of squealing noise and abnormal wearing of brushes. It is another objective of the present invention to provide a method for manufacturing such a dynamo-electric machine.
To achieve the objectives of the present invention, there is provided a dynamo-electric machine including a commutator secured around a rotatable shaft and a plurality of carbon brushes placed in sliding contact with the commutator. The commutator has a sliding contact surface placed in sliding contact with the plurality of carbon brushes. The sliding contact surface of the commutator has a plurality of peaks and valleys that are substantially regularly and alternately arranged in both axial and circumferential directions of the commutator. Alternatively, the sliding contact surface of the commutator may have a plurality of peaks and valleys that are substantially regularly and alternately arranged in the circumferential direction of the commutator.
Furthermore, to achieve the objectives of the present invention, there is provided a method for manufacturing a dynamo-electric machine including a commutator secured around a rotatable shaft and a plurality of carbon brushes placed in sliding contact with the commutator. The method includes a step of processing a sliding contact surface of the commutator, which is placed in sliding contact with the plurality of carbon brushes upon assembly of the dynamo-electric machine, to form a plurality of peaks and valleys in the sliding contact surface of the commutator with use of a cutting apparatus and a vibration generating apparatus. The plurality of peaks and valleys are substantially regularly and alternately arranged in both axial and circumferential directions of the commutator.